N = int(input())
S = input()
s = []
for i in range(N):
	s.append(S[i])
ans = 0
for i in range(N-4):
	if s[i+2] == "0":
		if s[i] == "0":
			s[i] = "1"
			ans = ans + 1
		if s[i+1] == "0":
			s[i+1] = "1"
			ans = ans + 1
		if s[i+3] == "0":
			s[i+3] = "1"
			ans = ans + 1
		if s[i+4] == "0":
			s[i+4] = "1"
			ans = ans + 1      
print(ans)